In transport systems, problems may arise due to uncertainty about the whereabouts of a vehicle and when the vehicle will arrive at a given location. Typically, the vehicle will either drop-off or pick-up a person or item at the given location.
This problem can arise with school buses, which pickup and deliver children at their homes or a nearby stop. In the morning, when the children are being picked up, they and their parents will be uncertain regarding the exact arrival time of the bus. Accordingly, the children must be at the stop location waiting for the bus before the bus is expected to arrive. If the bus is late for any reason, the children may be waiting in a cold or deserted area for an extended period of time. If the bus is ahead of schedule, or the children are late arriving at the pick-up spot, the bus may have to wait for the children, thereby delaying the subsequent pick-up of other children further along the route.
Problems may also arise when the bus is delivering the children at the end of the day, due to uncertainty regarding when the bus will arrive at a drop-off location. When parents arrive home, they may be uncertain whether the bus has in fact gone by, and whether or not their children have arrived home from school.
Prior art notification systems have been devised to address the above-noted problems. Generally, these prior art systems involve three-way communication between a bus, a central station, and each drop-off or pick-up location. Specifically, the vehicle first determines its location using, say, an onboard Global Positioning System (G.P.S.). Then, the vehicle communicates its location to a control unit at a centralized location. The control unit then determines the relative position of the bus in the route and notifies a series of receivers, located at or nearby the various pick-up and drop-off points, of the approach of the vehicle.
U.S. Pat. No. 5,400,020 discloses an advance notification system including a vehicle control unit for each bus, as well as a base control unit located in a centralized location. In operation, the vehicle control unit determines the location of the bus using a G.P.S. or other suitable system. The vehicle control unit then transmits this location information to the base control unit, which determines the relative position of the bus in the route from the absolute position determined by the G.P.S. When the bus is a certain predefined distance from a stop for a particular home on the bus route, the base control unit automatically telephones this home to inform the children or their parents that the bus is about to arrive.
While solving some of the above-mentioned problems, this system suffers from a number of disadvantages. The system depends on the centralized control unit, and if this centralized control unit fails, then the entire system will fail. The demands placed on the centralized control unit are considerable--it must keep track of each location to be notified of the approach of the vehicle. As a result, the centralized control unit is complicated and expensive, as is the G.P.S. or other suitable location system mounted on the bus. The system also ties up telephone lines, or, if the telephone line is in use, the message regarding the approach of the vehicle may not get through. Thus, an advance notification system that does not rely on a centralized communication system is desirable.